drive: Introduce kInitialChangestamp to DriveResourceMetadataTest

This is in preparation for adding tests that check the per-directory
changestamp to be zero, for newly added directories by RefreshDirectory().
In other words, we need to distinguish zero from the initial changestamp.

BUG=178348
TEST=none

Review URL: https://codereview.chromium.org/12706005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@187505 0039d316-1c4b-4281-b951-d872f2087c98
1 file changed